This invention relates to the preparation of unsymmetrical, substituted diphenylamines and a particular 3-methyldiphenylamine.
There has long been known procedures for the production of symmetrical, unsubstituted diphenylamines. Aniline is normally condensed in the vapor phase in the presence of a catalyst. Such processes are disclosed in U.S. Pat. Nos. 3,079,439 and 3,118,944. The production of diphenylamine from aniline in the liquid phase is disclosed in U.S. Pat. No. 3,205,265 wherein the reaction is catalyzed by a halogen and an oxygen containing compound of phosphorous.
It has also been disclosed in U.S. Pat. No. 1,885,355 that a symmetrical unsubstituted diamine such as di-beta-naphthol p-phenylenediamine could be prepared by reacting a diamine such as p-phenylenediamine with an excess of a substituted fused benzene ring reactant such as beta-naphthol.
More recently, there has been disclosed a process for the manufacture of diarylamines by the reaction of a phenol and aniline in the presence of a small concentration of sulfonic acid. Such process is disclosed in German Pat. No. 2,042,774. This patent suggests the manufacture of both symmetrical and unsymmetrical substituted diphenylamines in the presence of the acid catalyst. A continuous process is suggested through the use of interconnected autoclaves in succession whereby each autoclave is outfitted with a distillation column for the removal of water produced in the reaction. According to this process, the reaction operates with an excess of aniline. Under these conditions, the self-condensation of aniline leads to the formation of a substantial amount of by-product which is diphenylamine.
In yet another process described in Canadian Pat. No. 1,005,462, there is described a process for the production of diarylamines by the reaction of naphthol and a primary arylamine. In such process, ferric chloride is utilized as a catalyst. As in similar prior art, the primary arylamine is utilized in excess and therefore the formation of by-product by self-condensation of the primary arylamine is significant.
Generally, there is in the prior art relating to unsymmetrical, substituted diphenylamines a great tolerance for impurities in the final product, usually diphenylamine resulting from the self-condensation of aniline. The presence of such an impurity was probably of little concern because the end use of the product did not require high purity. However, there is a need to provide unsymmetrical, substituted diarylamines in high yield and purity when such amines are utilized as precursors for other products.